The invention relates to a dispenser with which flowable media may be released or discharged by pressurizing. Particulary liquid media, but also pasty, powdery and/or gaseous media are suitable. The dispenser is held and actuated single-handedly. The dispenser is primarily made by injection molding or of plastics. The medium may be discharged atomized, or delivered in discrete clusters or droplets having a volume of at least 5 or 15 .mu.l and at the most 40 or 25 .mu.l. The medium contains medicinal active substances for eye treatment, or the like.
Dispensers need to be microbiologically sealed to prevent the medium stored therein from being contaminated by germs gaining access from without. The medium needs to be protected from such detrimental effects during a long shelf life not only prior to first-time use (priming) of the dispenser but also after the initial or any following medium discharge. The dispenser may be for a single discharge of a medium dose in which its actuator is moved in one direction only up to the dispenser being totally emptied with no return or suction stroke being necessary. The total supply of the medium may be contained in a single delivery chamber, without any additional medium reservoir. The volume in the chamber is then variable for pressurized delivery of the medium. The dispenser or its actuator may also operate in two opposite direction via a working stroke for pressurized delivery directly followed by a return stroke for sucking a further medium dose into the delivery chamber. After discharge of a medium dose the microbiological seal is always able to be reproduced until the next discharge, which is not always necessary in the case of a disposable dispenser.
For this seal either a single valve or several valves may be suitable. The valves closing gaps are located in sequence in the flow direction in the outlet duct. The last or downstream valve is located as near as possible to the medium outlet or its opening bounds as formed by the transition between an inner circumference and an end face transversely adjoining this circumference. At this transition the medium detaches from all inner circumferences or internal dispenser faces for release to the environment. The medium may then still be guided downstream of the transition by accessible external dispenses faces.